LC photonic devices have found widespread commercial applications in a variety of fields ranging from spatial light modulators to photonic LC fibers because of their excellent tunability of refractive index with electric and magnetic fields. Switchable gratings are a type of LC photonic device that is useful for applications such as displays, beam steering, tunable filters, and telecommunication components.
A number of LC-based architectures have been proposed for switchable optical gratings. One class of liquid crystal gratings involves phase separation of a mixture of a liquid crystal and another material, typically a polymer, and exploits the refractive index difference between the background matrix and liquid crystal dopant. A second class of such gratings involves conventional patterned electrodes. Another approach to make switchable gratings is to use different alignment in adjacent grating portions. This approach includes two different alignment domains constructing the grating structure. These two different alignment domains could be the combination of a planar alignment domain and a homeotropic alignment domain, the combination of a planar alignment domain and a twist alignment domain, the combination of two planar alignment domains, etc.
Manufacturing cost and diffraction efficiency are critical issues with respect to switchable gratings. The existing LC-based architectures discussed above, particularly in the case of holographic polymer dispersed LCs gratings, have serious drawbacks, including expensive fabrication process, slow response time (about 2˜100 ms), scattering losses, and high driving voltages (>100 V).